Method for manufacturing a piston rod unit and a hollow shaft

ABSTRACT

A piston rod unit and a method for producing a piston rod unit, or a shaft, in light-weight construction, with a rod which is hollowly-drilled by means of a deep bore into the rod shank, and the resulting rod opening is closed subsequently by means of a forging process.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase of International PatentApplication Serial No. PCT/EP2017/000723 entitled “METHOD FORMANUFACTURING A PISTON ROD UNIT AND A HOLLOW SHAFT,” filed on Jun. 21,2017. International Patent Application Serial No. PCT/EP2017/000723claims priority to German Patent Application Serial No. 10 2016 007593.7 filed on Jun. 21, 2016. The entire contents of each of theabove-cited applications are hereby incorporated by reference in theirentirety for all purposes.

TECHNICAL FIELD

A piston rod unit and a method for producing the piston rod unit, aswell as a shaft, which is produced in accordance with such a method.

BACKGROUND AND SUMMARY

Piston cylinder units, such as hydraulic cylinders, are often used inlarge working machines. A predominant aim of the developers lies withthe optimization of the working machines in terms of overall weight, inorder to not only save production costs, but likewise optimize theefficiency of operation of the machines. Although the piston rod unitsmounted in the hydraulic cylinders contribute only a relatively smallpart to the overall weight, especially in large machine types, such asmining machines, significant weight savings can be achieved.

Most of the current developments aiming at a lightweight constructioncylinder provide a hollow piston rod construction, but the attachment ofthe hollow piston rod, which often is a simple pipe element, is effectedby means of screw- or weld connections to the piston rod head and thepiston. The drawback of this approach lies with the extremely negativeeffect of these connection types on the dynamic stress resistance of thelightweight construction cylinder. For this purpose, steel tempered andquenched with refractory metals having increased carbon equivalents maybe used, which achieve an increased strength due to the tempering andquenching of the steel, but can be welded poorly due to the solidifiedprecipitation phase in the steel. For this reason, the use of hollowpiston rod constructions, such as in hydraulic piston rod units formining machines, has not been possible so far, since the connectiontechniques used there on the basis of screw- and weld connections cannotbe combined with lightweight construction.

The object of the present disclosure thus is to provide an improvedmanufacturing method for a piston rod unit, which allows an optimumlightweight construction such as for mining machines.

According to the disclosure, it is proposed for the production of thepiston rod unit, to first hollowly-drill a piston rod by means ofdeep-hole drilling in the rod shank in order to ensure the desiredweight saving. The resulting rod opening of the deep-hole bore at therod end is closed-off by means of a forging process afterwards. Usingthis measure, the resulting closed piston rod is also suitable for usein heavy mining machines since the rod opening closed by the forgingprocess can be connected with the piston of conventional piston rodunits in conventional ways and manners. For instance, the resultingpiston rod can be connected with the piston through a simplescrew-connection. Open-die forging has proven as a suitable forgingmethod.

In some embodiments, the piston rod, including the piston rod head, maybe mechanically formed from a blank. By contrast to the prior art,piston rod and piston rod head are to be understood as a one-piececomponent, possible connections between the two sections of the pistonrod are omitted.

In the mechanical processing of the piston rod from a blank, forexample, provision is made for a process so that a material excessremains at the rod end of the piston rod. For instance, a materialexcess is left in the radial direction at the piston-side end of thetube-shaped piston rod. This material excess, in a correspondingthermo-mechanical stress during the forging process, is ideally used toblock the bore openings resulting from the deep bore. The materialexcess is consequently made to flow, due to the thermo-mechanicalstress, in the radial direction of the cylinder. As a result, it ispossible to close the bore opening at the rod end without having toemploy other connection techniques that have a negative effect on thedynamic stress resistance of the cylinder.

According to an embodiment of the method according to the disclosure, amandrel is inserted into the deep bore prior to beginning the forgingprocess, such as in the region of the bore opening at the rod end. Bymeans of the inserted mandrel, a precise closing of the bore opening inthe forging can be achieved, and thus a complete sealing of the cavityof the piston rod. Moreover, the entering material flow can becontrolled in better ways during the forging process.

The inserted mandrel can be in the type of a cylinder with asharply-tapering end. However, other geometrical shapes are alsoconceivable.

The mandrel can have a smooth surface structure. Alternatively, themandrel surface may also provide a non-smooth structure, e.g. with awave-shaped or another non-smooth profile. The quality of the closurecan be improved by means of a non-smooth surface structure of themandrel. As a result, it is ensured that the internal cavity is sealed,during each operating situation, against the intrusion of thenon-compressible hydraulic medium.

The bore end, i.e. the bore closing-off that ends in the piston rodshank, is of radial shape. An otherwise edged bore-cross-section at thebore end could lead to a potential notching effect.

The following assembly of the produced piston rod and a piston is forexample exclusively based upon a screw connection. As a result,potential weld connections inside the piston rod can be completelydispensed with, which leads to a significantly higher dynamic stressresistance of the entire piston rod unit. Since, by this approach, thestress resistance of the unit is optimized, higher weight savings can berealized in the manufacture in the end.

Besides the method according to the disclosure, the present disclosurealso relates to a piston rod unit that has been produced in accordancewith such a method. The piston rod unit thus provides the sameproperties as have been explained in more detail above by means of themethod according to the disclosure. For this reason, a repeateddescription is omitted.

Furthermore, the disclosure relates to the use, according to thedisclosure, of the piston rod unit in accordance with the presentdisclosure for a mining apparatus, such as for a mining excavator,ideally as a bucket cylinder.

Moreover, the present disclosure relates to a mining apparatus, such asa mining excavator with at least one piston rod unit, which ischaracterized in that the installed piston rod of the piston rod unit isof hollow design. The piston rod unit has been manufactured inaccordance with the method according to the disclosure. The miningapparatus is thus characterized by the same properties as have alreadybeen explained with reference to the method according to the disclosure.

BRIEF DESCRIPTION OF THE FIGURES

Further properties of the disclosure are to be explained in greaterdetail by means of an exemplary embodiment shown in more detail in thedrawings. The Figures show in:

FIG. 1: a hydraulic cylinder according to the disclosure, with a novelpiston rod,

FIG. 2: an image of an intermediate product in the manufacture accordingto the disclosure of the piston rod,

FIG. 3: the piston rod according to FIG. 2 after the effected forgingprocess, and

FIG. 4: the piston rod according to FIG. 2 after the effected forgingprocess in accordance with an alternative configuration.

DETAILED DESCRIPTION

The disclosure proposes a manufacturing method of a hydraulic cylinderin lightweight-construction. Construction according to the disclosureconsists in that potential weld connections inside the piston rod can becompletely dispensed with and required screw connections are reduced toonly one connection point between piston rod and piston. FIG. 1 shows acompletely-assembled hydraulic cylinder in the form of a differentialcylinder that has been produced in accordance with the method accordingto the disclosure. The hydraulic cylinder includes the cylinder housing10 with the piston rod 20 including piston 25 displaceably mountedtherein. The piston 25 is screwed to the piston rod end located in thecylinder 10 by means of a screw connection 26. Part of the screwconnection is the thread of the piston nut 27 located inside the piston25.

At the piston rod head 22, a boss for mounting the piston rod unit isprovided. The same applies to the closed cylinder end. To achievelightweight construction, the piston rod 20 comprises a deep bore 21,which extends in the longitudinal direction from the piston rod head 22to the mounted piston 25.

The manufacturing process of the piston rod unit first provides, in afirst step, producing the piston rod 20 including piston rod head 22from a blank in mechanical ways and manners. The piston rod 20 and thepiston rod head 22 are consequently made from one and the same startingmaterial, and are to be considered as a one-piece end product.Furthermore, during the machining process, a radial material excess 30is left at the rod end of the piston rod 20.

After that, the deep bore 21 is made from the rod end in the directionof the rod head 22 with the bore length B. The inner end 23 of the deepbore 21 is of radial shape, in order to thereby prevent a possible notcheffect by means of an edged bore cross-section. The resultingintermediate product is shown by FIG. 2. The piston rod has a length L.

The protruding material 30 is used, after the deep hole drilling 21, toclose the bore opening at the rod shank. This is effected by means ofopen-die forging or another, suitable forging process. In the forgingprocess, the protruding material 30 is made to flow, due to thethermo-mechanical stress, in the radial direction of the cylinder. As aresult, it is possible to close the bore opening at the rod shankwithout having to use other connection techniques that have a negativeeffect on the dynamic stress resistance.

Prior to the forging, a type of mandrel 40 can be laid into the bore 21(see FIG. 3), in order to be able to close and seal the bore openingprecisely and, on the other hand, be able to control the material flowduring the forging in better ways and manners. The proposed methodfurther allows acting more freely both in terms of the materialselection and the bore dimensions. This means that the yield in terms ofweight reduction can be increased due to the prevented weaknesses thatmight develop due to previous connection techniques. In large cylindersfor the field of mining, up to 400 KG can be saved.

In a further configuration, as shown in FIG. 4, it is also conceivableto configure the geometry of the mandrel 40′ in a wave-like or othernon-smooth form, in order to thereby increase the quality of theclosure. The internal cavity should be sealed against the entering ofthe non-compressible medium in each operating situation.

1.-9. (canceled)
 10. A piston rod unit comprising: a piston rod with arod shank, wherein the rod shank comprises a deep bore, and a piston,wherein the piston rod is form-fittingly connected with the pistonexclusively via an external connection type; wherein, the deep bore isformed by deep-hole drilling the rod shank and during drilling, amaterial excess is left at a rod end of the piston rod; and wherein therod end of the piston rod having the material excess has a greaterthickness than an immediately adjacent section of the piston rod. 11.(canceled)
 12. A mining apparatus, with at least one piston rod unit,wherein a piston rod of the piston rod unit is hollow.
 13. A miningapparatus comprising the piston rod unit of claim
 10. 14. The piston rodunit of claim 10, wherein the piston rod further comprises a piston rodhead, and wherein the piston rod, including the piston rod head, ismechanically formed from a blank.
 15. The piston rod unit of claim 10,wherein an end of the deep bore is of radial shape.
 16. The piston rodunit of claim 14, wherein the piston rod and the piston rod head are aone-piece component.
 17. The piston rod unit of claim 10, wherein thedeep bore extends in a longitudinal direction from a piston rod head tothe rod end of the piston rod.
 18. The piston rod unit of claim 10,wherein the external connection type is a screw connection.
 19. Thepiston rod unit of claim 18, wherein the screw connection comprises apiston nut inside the piston.
 20. The piston rod unit of claim 10,wherein the deep bore is closed by the material excess due tothermos-mechanical stress during the forging process.
 21. The piston rodunit of claim 10, wherein there is only one external connection pointbetween the piston rod and the piston.
 22. The piston rod unit of claim10, wherein the deep bore is completely sealed.